Generally, a circuit breaker is an electric protecting apparatus installed between an electric source and load units for protection of load units such as a motor and a transformer and an electric line from an abnormal current (a large current caused by i.e., short circuit and ground fault) generated at an electric circuit such as a power transmission/distribution line and private power transforming facilities. In other words, a circuit breaker is an automatic electrical switch that stops or restricts the flow of electric current in a sudden overloaded or otherwise abnormally stressed electrical circuit. A circuit breaker provides automatic current interruption to a monitored circuit when undesired over-current conditions occur. The over-current condition includes, for example, arc faults, overloads, ground faults, and short-circuits.
In order to break the line, the air circuit breaker is equipped with a stationary contactor and a movable contactor at a breaking mechanism where a current is made to flow in normal situation by connecting the stationary contactor and the movable contactor, and when there occurs a flaw at any portion of the line to allow flowing a large current, the movable contactor is instantly separated from the stationary contactor to open the circuit, thereby interrupting the flow of the large current.
A normal load current flows at a connected (service) position where the movable contactor and the stationary contactor are completely connected, where the circuit breaker is designed in such a manner as to sustain an impact force caused by short-circuit current for a predetermined time against the short-circuit current according to load capacity of the circuit breaker. The short-circuit current sustainable by the circuit breaker is detected by a trip relay and an actuator to trip an operating mechanism.
FIG. 1 is a schematic configuration of a typical circuit breaker in which a trip spring is compressed to allow a contact point to be turned off, FIG. 2 is a schematic configuration of a typical circuit breaker in which a trip spring is elongated to allow a contact point to be turned off, and FIG. 3 is a schematic configuration in which an over-current is applied to turn off the contact point in the exemplary implementation of FIG. 2.
Referring to FIGS. 1 to 3, the circuit breaker may include a movable conduction unit (3) rotatably coupled to any one terminal out of upper and lower terminals (1, 2), where a movable contact point is fixedly formed at a position in opposition to a stationary contact point mounted at the other terminal out of the upper and lower terminal (1, 2), and an operation mechanism (10) rotating the movable conduction unit (3) to allow the movable contact point to be connected to (ON) or be separated (OFF) from the stationary contact point.
Under the connected (ON) state, an open lever (23) and an open latch (22) are mutually connected to maintain an ON state in which the movable conduction unit (3) and the stationary contact point are contacted, and when a large current caused by flawed conditions (including, but are not limited to, current overload, ground faults, over voltage conditions and arcing faults) is detected, a trip solenoid (19) may rotate the open lever (23) to release the latched (meshed or contacted) condition between the open lever (23) and the open latch (22), thereby performing the OFF operation of separating the movable contact unit (3) from the upper terminal (1).
To be more specific, FIG. 1 refers to an OFF state of the contact point at the movable conduction unit (3) of the circuit breaker, in which an open/close axis (14) of the operation mechanism (10) is rotated to be brought into contact with an open/close axis stopper (18). A connection spring (56) is compressed by a rotating driver lever (16) due to rotation of a cam (12) caused by a motor or a manual handle (not shown), as illustrated in FIG. 1. The cam (12) in which the connection spring (56) is compressed may maintain equilibrium by an ON lever (20) contacting a connection latch (13). An ON coupling (17) contacting a connection button (25) or a connection solenoid (not shown) may be in a position that can rotate the ON lever (20).
When the ON coupling (17) moves down to rotate the ON lever (20), the connection latch (13) releases the cam (12), and force of the connection spring (56) is transmitted to a toggle link (15) through the driver lever (16), whereby the open/close axis (14) is rotated clockwise to expand an open spring (57) as illustrated in FIG. 2. The movable conduction unit (3) may contact the stationary contact point of the upper terminal (1) in response to the clockwise rotation of the open/close axis to conduct the lower terminal (2) and the upper terminal (2). Concurrently, a compression spring (58) is also compressed in order to allow the circuit breaker to have a resistance for a short period of time (capacity of conducting a short-circuited current for a second). The compression spring (58) applies a force toward the opening of the movable conduction unit (3).
As illustrated in FIG. 2, the equilibrium of the circuit breaker under the connected condition is maintained with the open latch (22) being latched to the open lever (23) through the toggle link (15) and a connection link (28). At this time, the OFF operation is such that, when the open lever (23) is rotated by an open button (26), an OFF plate or the trip solenoid (19), the open latch (22) is rotated to release the toggle link (15) toggled under the connected condition and to allow the open/close axis (14) to be counterclockwise rotated by the open spring (57) and the compression spring (58), causing the contact points to be in the OFF state as shown in FIG. 3. The cam (12) may be rotated again in order to compress the connection spring (56), as shown in FIG. 1.
If an over-current flows while the circuit breaker is in the connected condition, as shown in FIG. 2, an electro-impulsive (impact) force is generated by a current between the movable conduction unit (3) and the stationary contact point of the upper terminal (1) in response to the electro-dynamic compensation effect. The impact force may be transmitted to constitutional elements (parts) in various operational mechanisms (10) such as the toggle link (15), the connection link (28) and the open latch (22) via a transmission link (4).
Although the circuit breaker can withstand the impact force within the scope of the resistance for a short period of time with the assistance of the compression force of the compression spring (58) and the toggle link (15), but if a short-circuited current greater than normal flows in the movable conduction unit (3), a large impact force is transmitted to the operational mechanisms via the transmission link (4) to deform or do damage to the toggle link (15) before a trip relay (not shown) and the trip solenoid (19) release the open lever (23).